1. Field of the Invention
The present invention relates to an improved furnace and process for the feeding, mixing, suspension, calcining, reacting and/or melting of particulate batch materials in a combustion gas flow within a combustor, and for the continuous discharge of the combustion gases and the heat-treated or molten composition into a separation compartment to produce gas separation and high quality, homogeneous reacted and/or molten compositions. The invention is mainly concerned with the production of glass compositions but is applicable to any process in which particulate batch materials are being heated and/or melted while suspended in a combustion gas, and gaseous materials are being separated therefrom, such as calcining processes in which water vapor and carbon dioxide are released, melting ground glass cullet, vitrifying minerals, melting fiberglass scrap, etc.
2. Discussion of Prior Art
A wide variety of furnaces are known, such as for the production of molten glass from glass forming batch materials, which glass is fed into a molten pool while heat is applied to maintain a satisfactory temperature, such as about 1400.degree. C.
It is known to preheat and/or melt batch materials before their introduction to a molten pool, and reference is made to U.S. Pat. Nos. 3,443,921; 3,741,742; 4,135,904 and 4,816,056 for their disclosures of glass-making furnaces incorporating premelting or preheating means.
It is also known to heat the molten glass in a glass-making furnace by means of combustion gas jets directed from above the molten glass pool and/or to impart circulation to the molten pool and greater uniformity or homogeneity to the final glass. Reference is made to U.S. Pat. Nos. 3,489,547; 3,563,722 and 3,592,623 as well as U.S. Pat. No. 4,816,056 referred to above.
It is also known to introduce glass-forming batch materials to the glass-making furnace by feeding them into combustion gas burners for tangential discharge from the burner nozzles into an upper cyclone chamber of the furnace in which they are swirled and rendered molten before passing as a melt into the molten glass pool at the base of the furnace. Reference is again made to U.S. Pat. No. 3,563,722.
Such prior known glass-making furnaces are not as efficient as possible with respect to heat transfer, particle/gas separation and molten pool circulation and uniformity. Improvements in pool circulation result in more complete fining or gas bubble separation and greater uniformity of the molten composition and homogeneity of the formed glass.
Commonly-owned U.S. Pat. Nos. 4,617,042; 4,617,046 and 4,631,080 disclose methods of and apparatus for heat processing particulate material wherein finely pulverized glass batch material is heated very rapidly by preheating and mixing glass batch material in suspension in preheated oxidizer and/or fuel flow in an injector assembly, heating the glass batch material to a high temperature in the burner assembly, directing the products of combustion and high temperature batch material suspended therein through an accelerating nozzle, to form a downwardly directed linear flow having a small cross-sectional area, and causing the accelerated flow exiting from the nozzle to impact on a solid impact surface above the molten pool, the high temperature batch material adhering to this impact surface and then flowing down its sides to the molten pool.
In accordance with the aforementioned Patents, glass batch material is heated in suspension in the products of combustion to a condition at which it can form a flowing layer on the solid interposed impact surface and rapidly react to form glass product. The impact body provides the multiple function of separation of the glass batch material from the products of combustion, fining and at least substantial reaction of the constituents of the glass batch material.
In addition to efficient heat transfer, highly effective glass fining is provided by a thin flowing melt layer having strong internal shear motion. Thus, prior art fining agents, such as sulfates, are not required, which eliminates a source of SO.sub.x pollutant emission. The inventions of the Patents also allow accurate control of combustion stoichiometry, so that carbon addition to the batch, as would normally be required for reduced flint glass production, is not necessary.
Among the problems encountered with such furnaces is the difficulty in obtaining a uniform particle distribution and suspension throughout the combustion chamber, or in obtaining the necessary duration of suspension to produce uniform heating and/or melting of particles of various sizes, or in obtaining high batch loading or throughput while retaining the necessary temperature of the combustion gases and producing the desired temperature quenching to reduce the formation of NO.sub.x pollutant gases.